Automatic control for aircraft equipment



Feb. 22, 1944. c. c. FAWCETT AUTOMATIC coN RdL FOR AIRCRAFT EQUIPMENT mWF 4 v S N vFiled May 20, 1940 ATT ORNEY Feb. 22,1944;

c.'c. FAWCETT 7 2,342,184 AUTOMATIC CONTROL FOR AIRCRAFT EQUIPMENT FiledMay 20, 1940 INVENTOIR r CHARLES C.FAWCEH' W m ATTORNEY 4 Sheets-Shet 2Feb. 22, 1944. c, c, FAWCETT 2,342,184

AUTOMATIC CONTROL FOR AIRCRAFT EQUIPMENT Fiied May 20, 1940 4 Sheets-Sheet s CHARLES C. FAWCETT A-rw-manzv Feb. 22-, 1944.

c. c. FAWCE'TT 2,342,184 AUTOMATIC CONTROL m AIRCRAFT EQUIPMENT FiledMay 20, 1940 H 4 Sheets-Sheet 4 INVENTQR" CHARLES C. FAWCETT ATTORNEV 3been left entirely to Patented Feb. 22, 1944 AUTOMATIC CONTROL FORAIRCRAFT EQUIPMENT Charles C. Fawcett, Sackville, lilew Brunswick,Canada Application May 20, 1940, Serial No. 336,241 4 Claims. (01.12.1-46.5)

Introduction 7 This invention relates to an apparatus for ex- -ertingautomatic control of aircraft equipment.

Specifically, the invention provides apparatus for controlling, inresponse to the true air speed of the craft or its altitude, equipmentwhich the pilot customarily operates manually. Generally speaking, thisequipment includes means responsive to the ratio between the dynamicpressure set up by the speed ofthe plane and the static barometricpressure for converting this ratio into movement, in combination. withmeans for amsubject to automatic control for this purpose are thefollowing:

1. Oxygen supply apparatus. 2. Cabin air compressors.

3. The engine supercharger. 4. The variable pitch airscrew.

' 5. Carburetor altitude control.

6. Etc.

Objects Having regard to the foregoing, it is a principal object of theinvention to provide apparatus repllfying the movement to initiateoperation of the equipment.

The problem Prior to this invention certain aircraft contro1s,"eitherdirectly or indirectly dependent on air speed for the timing of theiroperation, have the Judgment of the pilot.

The operation of such controls usually occurs during the landing andtake-off period when the pilot is pre-occupied with precision flyingpermitting him all too little time for attention to secondary aircraftcontrols. 1

With the increase in complexity and number of controls, it becomes moreandmore important that the human element be eliminated by the provisionof automatic means for operating them.

Pieces of equipment which the pilot generally controls manually at agiven airspeed and to which automatic control could advantageously beemployed, are as follows:

1. The retractable undercarriage.

2.. Flaps.

3. Wing slots. I

4. The variable pitch airscrew.

5. Carburetor controls.

6. The engine boost.

'7. Air brakes, particularly for dive bombing. 8. The retracting gearfor wing tip floats.

9. Retractable seaplane float rudders. 10. Apparatus for impartinginitial rotation-to the landing gear wheels prior to landing. ll -Etc.

Pieces of equipment which the pilot generally operates manually at givenaltitudes or at given barometric pressures, and which could also bewhich the invention sponsive. to'airspeed for the automatic control ofcomponents and equipment of aircraft. It is a further object to provideapparatus of this nature which issimple, reliable in operation, eco-'nomical to manufacture and to install ern aircraft. It is a invention toprovide a compact control unit embodying the working parts of thisapparatus ready for simple installation in a modern aircraft.

' With these and "other objects in view the invention may convenientlyemploy, to initiate control, ari instrument responsive to thelatio beinmodtween the dynamic and static pressures, calibrated s so as, at agiven airspeed or barometric pressure as the case may be, to set a Servounit in operation. This unit amplifies the movement of the instrumentinfurnishing adequate force to ensure operationof a further valvecontrolling the direction of flow of hydraulic pressure,

Drawings This general description will be better under stood byreference to the accompanying drawings illustrating preferred forms ofapparatus in is embodied and in which: Figure 1 is a diagrammatic viewof this preferred form of apparatus, showing the elements in theposition they assume prior to their response to a predeterminedairspeed. Figure 2 is a diagrammatic view of the apparatus shown inFigure 1 with the elements in the position they assume after response tothe predetermined airspeed.

Figure 3 is a diagrammatic view showing three airspeed-sensitiveautomatic controls responsive respectively to different airspeeds, forcontrolling different pieces of aircraft equipment, namely still furtherobject of the centre line 44 of of the bellows 80 and GI equipment. Theconnection the retractable undercarriage, aerodynamic flaps and slats,and the air-screw pit'ch setting.

Figure 4.is a cross section taken through the Figures 5 and 6 of apreferred piece of equipment embodying the elements illustrateddiagrammatically in Figure 1 and 2. Figure 5 is a cross section throughthe piece of equipment of Figure 4 taken transversely of the latter atthe line 5-5, on Figures 4 and 6. Figure 6 is a section of the equipmentshown in Figures 4 and 5 taken through the centre line 66.

Figure 7 is a diagrammatic'view illustrating the application of thepreferred form of apparatus shown in the previous figures, to anelectrical control.

General arrangement I The general arrangement and principle of theapparatus may be gathered by referring to Figures 1 and 2 of thedrawings. l represents an electrically heated Pitot head mounted at theleading edge of a wing and having an opening II for picking up dynamicpressure in response to the speed of the craft and another opening l2for static or barometric pressure.

The Pitot head I0 is connected as in conventional airspeed indicators,by dynamic and static pressure lines l6 and I1 respectively, to aninstrument for converting theratio between the dynamic and staticpressure into movement, in this case a Sylphon or bellows 30. A heater Icontrolled by a thermostat is provided to heat the static pressure lineI! so as to keep the air circulating in the bellows housing at aconstant temperature, so as to free this instrument from temperaturevariation. The moveable wall of this bellows is connected to the stem 40of a sliding valve controlling a pressure system which, as will bedescribed, operates the twin bellows 60 and SI of a Servo unit.

Pressure is induced'in the Servo unit by a vacuum pump 80. A pressureline 8| leads from' the vacuum pum to the chamber 42 of the valve 40through the movement of which it may be connected to the housing ofeither bellows 60 or 6i through pressure lines 82 and 83 respectively.Openings 62-and 83 connect the inside with the atmosphere. The twinbellows 60 and GI are connected to the stemof the sliding valve IIIwhich is the main control valve for controllingthe direction of flow ofoil to hydraulic jacks operating the of the instrument with variouspieces of equipment can be seen in Figure 3 and will later be describedin detail. The hydraulic system includes an oil pum lflfi receiving itssupply-from an oil tank IM.

sure lines 9| and 92 lead from the housing of i the valve 10 to ahydraulic jack on the particular niece of equipment. Flow in duced bypressure from the oil pump throu h a supply line 102 and a return lineI03, the direction of flow in the lines 8| and 92 being governed by theposition of the valve 10. That is tosay, when the valve Ill is in theposition 'of Figure 1,' there is a positive now in the line 9i and a.retum flow in the line 92 and, when the valve is in the position ofFigure 2 the opposite is the case. When the equipment is static in theoperative or non-operative position the oil merely passes through arelief line I05 past a relief valve I06 back to the tank Illi,

, static and the bellows these lines is in- Operation tion of thelanding gear. When the craft is flying at a low speed the dynamicpressure on the Pitot head is substantially balanced by the staticpressure and the bellows 30 remains in the contracted, position ofFigure 1. When, however, the airspeed increases to a predetermined rateto which the bellows 30 is calibrated, say M. P. H., the dynamicpressure overcomes the 30 is expanded into the position of Figure 2.This moves the valve stem 40 into the position of Figure 2 causing theair to be exhausted from the housing of the bellows 6i, neutralizing thepressure in the bellows 60 by admitting atmospheric pressure both intothe housing and into the bellows itself. This causes the valve stem 10to move into the position of Figure 2. This the oil flow in the lines 9|and 92 causing the hydraulic actuating means of the undercarriage tooperate in retracting it.

If it is desired to use the matic control at given altitudes, as forinstance for control of pieces of equipment mentioned above, it will bemerely necessary to seal oil from the inside of the bellows the dynamicpressure line l6 and to calibrate the instrument so that static pressurealone operates the bellows at a certain altitude.

By this arrangement the load imposed'on the main hydraulic systemcontrol v'alvelll is all taken up in the twin bellows 60 and 6| of theservo unit. Considerable force is available for operating these bellows,from the forced pressures,set up by the vacuum pump 80. This relievesthe servo unit control valve and consequently thesensitive bellows 30responsive to c and atmospheric pressure, from any load. By reference tothe figures it will be seen that, owing to the construction of the valveIII, the pressures on opposite sides of its pistons are Automaticcontrol of various pieces of equipment Figure 3 illustrates the paratusdescribed in conjunction with Figures 1 and 2 to the operation ofvarious pieces of equipment. In this figure, the Pitot head I0 is shownconnected to three units F, (3' and H, each embodying an in Figures 1and 2. For changing the direction of flow of oil pressure directly inrelation to airspeed, the dynamic and static pressure lines I! and I1respectively are connected in parallel to these units. The otherelements of the apparatus are denoted by the same numbers as inconnection with Figures 1 and 2, for instance the immediately causesreversal of instrument for auto-' application of the ap-' arrangementsimilar to that described operated by g 2,842,184 vacuum pump 80, theoil lines 8|, 02, I02, I03,

I05, etc.', the oil tank IN, and the pump I00, etc.

J represents a retractable undercarriage a hydraulic jack IIO to whichhydraulic pressure controlled by the unit F is supplied to the lines 9|and 92. The unit F is so calibrated that, at 100 M. P. H., the pressurein the lines 9| and 92 is reversed and the piston of the hydraulic jackforced upwards, retracting the undercarriage. When the speed falls below100M. P. H., the fiow is reversed.- again and the undercarriage movedback into the position indicated in the full lines -of the figure.

K represents aerodynamic flaps and L aerodynamic slats. Oil lines I andI2I lead from I21 which controls the slats L. The unit G is calibratedso that at l20 M. P. H. the oil flow in the unit G to connections withoil lines I22 and the lines I20 .and I2I is reversed, as a resultreversing the disposition of the piston in the jacks I24 and I21respectively-so that the slats and flaps are moved into thepositionshown in dotted lines. I v

M represents a two-piece airscrew. Lines I and I3I carry hydraulicpressure from the unit H and to a jack I34 operating apparatus I35 forchanging the pitch of the airscrew. As indicated this apparatus I35 canalso be operated manually by the over-control I36. The unit H iscalibrated so that at 150 M. P. H. the flow in the lines I30 and I3I ,isreversed and the pitch of the airscrew changed to ahigh-pitch setting.

When the speed falls below 150 M. P. H. the flow is reversed again andthe pitch of the screw changedback to a low-pitch setting.

Preferred control unitstructure The working parts of the controlapparatus proper shown diagrammatically in the previous figures canconveniently be embodied in a compact unit all ready for simpleinstallation in an aircraft. This unit is accommodated in a housing Ifor the main bellowsv and a casing I80 for the Servo unit. the casinghaving an extension I8I fitting within a part of the housing. Thisextension includes a large centrally arranged cylindrical recess, intowhich there fits a special passage-forming housing I00 for the Servounit control valve 40. All the connections indicated in Figures 1 and 2between the air or hydraulic lines and the Servo and main control valvechambers are made by way of cooperating orifices in the housing I50,casing I80, or in the special passage-forming housing I80. Thisimportant structure will be described in further detail. The end of thecasing I50 is provided with an opening permitting the insertion of ascrewthreaded adjustment-retaining ring I5I, held in place by screwsI52. Into this ring is screwed a hollow adjustment screw I53, providedon the outside with a right-hand, and on the inside with a left-handthread. Into the adjustment screw is inserted a tubular dynamic pressureconnection 154 to the bellows, which is provided outside with. aleft-hand thread and which has inside a threaded pipe connection I forthe dynamic pressure line. A threaded pipe connection I 6I is providedin the bellows housing I50 for the attachment of the static pressureline. A locking nut I56 is provided to hold the adjustmentscrew I53 fromrotation. The bellows 30 is mounted on the end of the dynamic pressureconnection I54. A plate I63 reinforces the end of the bellows and alsoincludes a. notched protuberance I64 to engage a rib I65 on the casingI50 so as to retain the bellows from rotation during calibration andadjustment. The bellows is metallic and calibrated to expand under apredetermined pressure. The movable end of the bellows 30 is connectedto a small housing I6I screwed to the stem 40 of the valve controllingthe Servo unit. A plate I66 reinforces the movable end' of the bellows.

The extension I8I slides into the casing I50 and is held in place byscrews I82. A gasket I83 completes a pressure-tight connection betweenthe two casings. The Servo unit control valve housing I90, fits into therecess I84 of the ex'- tension I8I held in place by a retaining ring I9Iscrew-threaded to the extension'at the end of the recess.

Special valve housing The housing I is of a special constructionbelieved to be novel, consisting of a. cylindrical casting machined toan exact fit in the recess .I84 and otherwise formed as follows. Toaccommodate the piston of the sliding valve 40, the

' housing is provided with an axial boring 200 in which is inserted thecylindrical sleeve 42, pref erably of stainless steel constituting achamber in which the valve piston is freely movable. The

i'it of the valve piston is such that it will under all conditionsmovevery freely within the sleeve. The upper end of the .sleeve isprovided with projections 202 limiting the movement of the valve pistonin the upward direction while movement in the downward direction islimited by the base of the cylindrical recess I84.

In order to provide the necessary connections between the valve chamberand the air lines the housing is formed as follows. First, it isprovided with a series of circular grooves 2"! to 2 I4, the groovesbeing machined out on a lathe, with the top and bottom grooves slightlydeeper than the intermediate three grooves so that they can beinterconnected by a longitudinal boring 220, which clears theintermediate grooves. The outer end of this boring is sealed by agrubscrew 22I.

Each groove is connected with the valve chamber by its respective radialboring 2I0a to 2I4a. These small diameter borings are accurately placedin a longitudinal direction with respect to the valve chamber as themachined circular grooves act as a guide for the small diameter drillused to form the radial borings. This method greatly facilitatesmanufacture of a compact unit. The groove 2 I 0 registers with a radialboring 230 in thebuter casing which in turn registers with alongitudinal boring 233 having a pipe connection 234. This connectionopens to the atmosphere. The radial end of the boring 230 is sealed by agrub-screw 23I. Similarly the groove 2 registers with a radial boring240, which is joined to the housing of the bellows 60 by a diagonalboring 242, the radial end of the boring 240 being closed by agrub-screw 2".

In a like manner the groove 2I2 registers with The grub-screw Iii closesthe end of the radial groove 269.

The groove Ill connects with the groove liil by the longitudinal boringm in the housing with this structure it can readily be seen that thehousing I90 fulfils the function of completing the connections betweenthe valve chamber 42 ,and the lines leading through the casing I80. tothe respective elements of the Servo unit.

The stem 60 of the Servo unit control valve carries end pistons 45 and48, and a centre piston '0. which serves to make or break the pneumaticline connections, as in the manner of a sliding valve and as will beclearly seen by reference to Figures 1 and 2.

The lower part (in the position of Figure 4) of the casing I80 ismachined out to form the chamber of the bellows 80 and Hi. The outer endof each bellows is mounted on a diaphragm 219 provided with thecentrally arranged orifice 2' open to the atmosphere. The diaphragm 270is mounted by means of a' gasket 212 and retaining ring 213,screw-threaded into the end of the bellows chamber. The movable end ofeach bellows is provided with a housing 280 screw-threaded to the stemvalve it.

T'he chamber of the main control valve is formed by a boring 2Mextending between the two bellows chambers and lined with a stainlesssteel sleeve 282. The oil return duct is formed by a boring 800 betweenthe two bellows chambers and sealed off at each end by grub-screws 362and 808. the valve chamber by transverse borings 3M and B05 sealed offfrom the outside of the casing by grubscrews 306 and 807. The boring 860is connected to the oil return pipe fitting am by a diagonal boring 8ii.

The oil pressure supply pipe connection SIB is connected to the valvechamber by a longitudinal boring Sit. while the jack connections withthe valve chamber are made through pipe connections 320, Mi leading torespective borlngs $22 and 823.

The stem iii of the main control valve for the hydraulic system includesend pistons and I8, and a centre piston 11. which serves to make orbreak the hydraulic connections. as in the manner of a sliding valve andas will be seen clearly by reference to Figures 1 and 2.

boring being connected with the iii of the main control Lugs 330. areprovided for mounting the control unit to the aircraft, as for instanceunder the pilots floor. or in any other suitable position. The operationof this unit will be best "gathered by referenceto the diagrammaticrepresentations of Figures 1. 2 and 3 and the attendant description.

' Electric control The application of the invention to gontrollingelectrically-operated equipment is s own diagrammatically.The'ueleinents of the Servo unit common to the hydraulic control havebeen numbered correspondingly. In this electrical control, however, thetwin Servo bellows til and ti. instead of being associated with ahydraulic valve are connected to the respective ends of an electricswitch bar 350 moveable axially of an insulated switch housing M6. Theswitch bar is provided with male contacts 853 and 354 which. on movementof the valve. engage with female contacts 855 and 858 or 858 and 351, asthe case may be. The contact 885 has a positive con nection, the contact857 a negative connection and 388 a neutral connection. Movement of theswitch between the contacts causes a reversal of flow of the current inthe circuit actuating the control for the equipment being operated.

Advantages The compactness of the particular unit described makes itpossible to mount it in a very small space; it is also very light inweight. By the nature of its structure the unit requires no attentionexcept for the normal periodical instrument check-up. In operation, itwill function smoothly and reliably, removing considerableresponsibility from the shoulders of the pilot at all times,particularly when he is pre-occupied with precision flying. Noadditional equipment is required with the preferred unit.

It will be understood that various other modifications may be made inthis invention without departing from the spirit thereof or the scope ofthe claims. and therefore the exact forms shown are to be taken asillustrative only and not in a limiting sense. it being desired thatonly such limitations shall be placed thereon as are set forth in theaccompanying claims.

The sub-titles used throughout the specification are merely to simplifyreference thereto and should otherwise be disregarded.

I claim: Y

1. In a unit for controlling aircraft equipment a casing. a main slidingcontrol valve for said equipment mounted in said casing. said casingbeing formed to include a bellows housing at each end of said controlvalve. a bellows in each housing connected to a respective end of saidcontrol valve. an atmospheric pressure passage to theinterior of each ofsaid bellows, a cylindrical boring in said casing. pressure supplypassages between each bellows housing and the walls of said boring. avacuum pump. pressure supply passages from the wall of said boringleading to said vacuum pump. a passage from the wall of said boringleading to an atmospheric pressure connection, a cylindrical valvehousing inserted within said boring. said valve housing including anaxial passageforining a valve chamber. openings in said valve housing tocomplete communication between said chamber and each of said pressuresupply passages. an additional opening in said housing leading from saidvalve chamber to the atmospheric pressure passage. a sliding pressurecontrol valve in said chamber for controlling said pressure supplypassages and pressure responsive means for actuating said slidingpressure control valve whereby control is exercised over said maincontrol valve. I

2. An apparatus as claimed in claim '1 wherein the passages in saidvalve housing are formed by a plurality of circular grooves therein.borings extending between said grooves and the valve chamber. one pairof grooves being outside the other grooves and deeper. and alongitudinal boring connecting said outside grooves without touching theother grooves. the outside grooves communicating with the passageleading to the atmosphere.

3. In a unit for controlling aircraft equipment, a compact casing. amain sliding control valve for said equipment mounted in ing beingformed to include a bellows housing. a bellows in said housingoperatively connected to said control valve, a recess in said casing. avalve housing inserted within said recess. said valve housing including"an axial a valve chamber,

passaBe forming ing from thebeiiows housing to the wall ofplvv passagesleading from the wall of the recess to said pressure supply connections,openings in said valve housing constituting communications between saidvalve chamber and each of said' pressure supply passages, said openingsand pressure supply passages permitting fluid pressure to be transmittedfrom said pressure connections to said bellows. a sliding pressurecontrol'valve'in said chamber for controllini the communication .acommunication passage lead-- the.

recess, pressure supply connections, pressure supin said recess iscircular,

grooves and valve chamber.

between the respective openings thereby to control communication betweenthe pressure supply connections and the bellows, and pressure responsivemeans for actuating said pressure control valve thereby to exercisecontrol oversaid main control valve.

4. An apparatus, as claimed in claim 3, whereand said valve housingcylindrical, the passages in said valve housing being formed by aplurality-oi circular grooves therein, and borings extending betweensaid CJFAWCEIT,

